1. Field of the Invention
The present invention relates to a method for determining the flying height of a magnetic head used for writing information to a magnetic disk and/or reading information from a magnetic disk, and a method for controlling the flight of a magnetic head.
2. Description of the Related Art
A magnetic head, such as a hard disk device, is arranged at an interval relative to a surface of the rotating magnetic disk, and information is written to the magnetic disk and/or is read from the magnetic disk. Recently, in association with high density recording on a magnetic disk, the interval between the magnetic head and the surface of the magnetic disk (a flying height of the magnetic head) is extremely small, and is set at, for example, 10 nm or less. When the flying height of the magnetic head is very small in such case, if the flying height of the magnetic head varies for some reason, there is a possibility that the magnetic head may make contact with the surface of the magnetic disk and that the magnetic head may be damaged. Therefore, in order to control the magnetic head so as not to make contact with the magnetic disk, it is desirable to obtain the flying height of the magnetic head.
In the method described in U.S. Pat. No. 5,130,866, the reading output (read back signal) is obtained by reading data signals (magnetic transition) pre-written at a pre-selected position on a magnetic disk by a magnetic head. The reading outputs are obtained under two conditions with different flying heights of the magnetic head, respectively, and the difference in the flying height of the magnetic head under the two conditions can be obtained by using the known Wallace equation (described hereafter).
In this case, the difference in the flying height (a relative value) can be obtained between the two conditions with different flying heights of the magnetic head. However, the flying height (an absolute value) of the magnetic head, i.e., the interval itself between the magnetic head and the surface of the magnetic disk cannot be directly obtained. In order to obtain the flying height of the magnetic head under specific conditions, i.e., the interval between the magnetic head and the surface of the magnetic disk, first, the reading output under the specified condition is obtained. Then, the magnetic head is intentionally brought into contact with the surface of the magnetic head, and the reading output is obtained under contact conditions. This enables comparison between the condition where the flying height should be determined and the condition where the flying height of the magnetic head is zero. As a result, the flying height to be determined can be acquired.
Even in the inventions described in U.S. Pat. No. 7,589,928 and US Patent Laid-Open Publication No. 2008/94755, a magnetic head is brought into contact with the surface of a magnetic disk and the reading output is obtained, and the flying height of the magnetic head can be acquired by comparing the reading output obtained under the contact condition with the reading output in the condition where the flying height should be detected.
These methods all use a technique for obtaining the difference in the flying height of the magnetic head under two conditions. Therefore, in order to obtain the flying height of the magnetic head under a particular condition, it is necessary to acquire the reading output under the condition where the magnetic head is brought into contact with the surface of the magnetic disk. This means that the magnetic head collides with the magnetic head every time the flying height is obtained, and there is a risk of damaging the magnetic head and the magnetic disk.
Further, in these methods, the flying height of the magnetic head is calculated based on the reading output of pre-written data signals. Therefore, the magnetic head must have a reproductive element part (reading part), and when obtaining the flying height, it is necessary to activate the reproductive element part. Then, in the case of adopting these methods, it is necessary to write a predetermined data signal into a predetermined position on the magnetic disk. The reasons are because there is a possibility where the flying height based on the reading output may not be accurately calculated if the details of the data signal are unknown, and the data signal cannot be easily read by the reproductive element part if a writing position of the data signal is unknown. Thus, a specific region (contact lane) to be used for acquiring the flying height must be established and a specific data signal must be written. In the case of using a general magnetic disk not having such a specific region and specific data signal, the flying height of the magnetic head cannot be acquired and the magnetic head cannot be controlled so as not to come into contact with the surface of the magnetic disk.
In US Patent Laid-Open Publication No. 2008/007871, a sensor for detecting contact of a magnetic head with a magnetic disk is disclosed. Specifically, an acoustic emission sensor or a thermal asperity effect element sensor is arranged on an air bearing surface of a slider including the magnetic head. The sensor detects contact between the magnetic head and the magnetic disk based on the friction when the magnetic head makes contact with the magnetic disk. Although such a sensor is broadly adopted to a common magnetic head, it cannot prevent the magnetic head from making contact with the magnetic disk before such contact occurs, and the sensor does not have the effect of preventing breakage of the magnetic head.
In US Patent Laid-Open Publication No. 2008/0043355, US Patent Publication No. 2008/94755, US Patent Publication No. 2008/007871 and Japanese Unexamined Patent Application Publication 2008-77751, methods for approximating the distance of a magnetic head to a surface of a magnetic disk by thermally expanding at least a portion of a slider by driving a heater placed in a slider where a magnetic head is formed for generating heat are described. In this case, it is possible to minutely adjust the flying height of the magnetic head by adjusting the driving power of the heater. The heater (heat-generating resistor) in Japanese Unexamined Patent Application Publication 2008-77751 also functions as a sensor for detecting collision of the magnetic head against the magnetic disk.
In U.S. Pat. No. 7,589,928, a system having a magnetic device for writing to a magnetic medium and reading from the magnetic medium, and a sensor arranged adjacent to the magnetic device so as to be close to the magnetic medium is disclosed. The sensor generates a signal relating to a change in heat within the sensor, which is generated due to a change of the interval between the magnetic device and the magnetic medium.